This invention relates to method and equipment for assessment of patient support systems.
Pressure on the human skin leads to triaxial distortion of the skin and the underlying tissue and comparison and distortion of tissues against the bony skeletons. As a result, the blood vessels which are in these tissues become distorted and this leads to a diminution of the blood supply causing ischaemia with resultant tissue necrosis. This is manifest by the development of pressure sores which, if not carefully treated, do not heal but become chronic and more and more extensive. The problem is particularly prevalent in patients who are elderly or disabled and confined for long periods to bed or to a wheelchair.
Frequently, patients admitted to hospital develop pressure sores during their treatment, and the additional nursing cost of treating pressure sores is considerable.
In one recent study (see A. B. Ward, Prescriber's Journal, 30(6) 1990), it was stated that between 3 and 11% of all patients admitted to hospital develop a pressure sore, and the average duration of treatment for those with significant lesions is 51 days at an estimated cost of .English Pound.26,000. It has been estimated (see Turner, Wound Management, 1(1), April 1991) that the care of patients suffering from pressure sores is costing the National Health Service as much as .English Pound.200,000,000 per annum.
A variety of patient support devices and equipment have been developed in an effort to prevent, and/or assist the recovery from, pressure sores. The cost of such equipment varies widely and various claims are made for their effectiveness by the manufacturers and distributors. However, there is no proper basis for assessing the value of these claims or the effectiveness of the equipment, since there are no generally accepted protocols or methods for the evaluation and comparison of patients support systems.
While clinical evaluation has been carried out on behalf of individual manufacturers of equipment and by researchers, the number of patients observed in these tests have been too small for proper statistical evaluation. Another approach has been to directly measure the interface pressure between a support surface and the patient, but such measurements are confounded by experimental and repeatability errors, e.g. because of the difficulty of accurately placing a pressure transducer at precisely the same point when testing two patients support surfaces with a given patient. Another difficulty is that measurements can vary as a result of changes in temperature and moisture levels. Further, the use of patients and volunteers makes comparison of various workers findings virtually impossible since the viscoelastic properties of patients and volunteers' tissues of various ages is variable. The same groups of patients and volunteers cannot be available at all times world-wide which would be required for accurate comparisons.